Computers and other devices are commonly interconnected to facilitate communication among one another using any one of a number of available standard network architectures and any one of several corresponding and compatible network protocols. Packet switched network protocols are commonly employed with a number of architectures such as the Ethernet® standard. One of the most basic and widely implemented network types is the local area network (LAN). In its simplest form, a LAN is a number of devices (e.g. computers, printers and other specialized peripherals) connected to one another over a common broadcast domain using some form of signal transmission medium such as coaxial cable. Multiple LANs may be coupled together as two or more sub-networks of a more complex network via routers or equivalent devices, each of the LANs having a distinct broadcast domain.
Computers and other devices employ network resources as a requisite interface with which to communicate over a network such as a LAN. These network resources are sometimes referred to as network adapters or network interface cards (NICs). An adapter or NIC typically has at least one port through which a physical link may be provided between the processing resources of its network device and the transmission medium of a network. Data generated for transmission by the processing resources of one network device is first formatted (as packets in the case of packet switched networks) in accordance with its resident protocol layer (a software process typically executing in conjunction with the device's OS (operating system)). These packets are then framed and transmitted through the device's network resources, over the transmission media to the network resources of a second network device similarly coupled to the network. The data received by an adapter port of the second device is passed to and then deformatted by the protocol layer resident in the O/S of the second network device. The deformatted data is presented to the processing resources of the second device. The adapters or NICs are commercially available and are designed to support one or more variations of standard network architectures and known topologies, including Ethernet as described above.
In an Ethernet environment, each network device and its links to the network are identified by the other devices on the network using a protocol address (e.g. Internet Protocol (IP)) and a media access control (MAC) address in accordance with layer 3 and layer 2 of the OSI networking model respectively. The protocol address is associated with a virtual interface established by software between a device's adapter hardware and the protocol layer executed by its OS. The MAC address is uniquely associated with the adapter hardware itself and is typically hard-programmed into each device at the time of manufacture. Provision is often made such that this pre-assigned MAC address can be overwritten through software command during initialization of the device. Devices coupled to a common broadcast domain of an Ethernet network identify each other by the MAC address. Devices coupled to disparate broadcast domains communicate using their IP addresses over a device such as a router that couples the two domains.
Thus, a network device such as a server can be directly coupled to one or more physical networks or sub-networks through one or more distinct adapter ports coupled to each of the one or more networks or sub-networks. Each adapter port and its associated protocol interface are identified by a unique MAC address and IP address respectively. In the alternative, a single adapter port may be coupled to a special switch that can be programmed to provide connections to devices belonging to one or more logical sub-networks called virtual LANs (VLANs). The VLANs are essentially superimposed or overlaid on the same physical network to create multiple logical networks sharing the same physical broadcast domain. A virtual interface to the device's protocol layer is created for each of the VLANs and thus each VLAN virtual interface is assigned its own protocol address. The single adapter port, however, is still known to the devices comprising the various VLANs by a single MAC address.
To improve the reliability of a network, redundant links have been established with the same network through multiple adapter ports in the event that one of the links fails. Redundant links can also provide an opportunity to increase throughput of the connection through aggregation of the throughput through the redundant links. Redundant links to the same network can be established through multiple adapter ports coupled to a network switch for example. This is sometimes referred to as multi-homing. While providing some of the benefits of redundant links, implementation of multi-homing to achieve redundancy is difficult for reasons known to those of skill in the art.
Redundant links can also be accomplished by teaming two or more adapter ports together to appear as a single virtual link. Adapter teams are typically made up of two or more adapter ports logically coupled in parallel using a teaming driver. The teaming driver is a software routine executed by the OS that presents a common virtual interface to its protocol layer for the entire team of resources rather than individual interfaces for each adapter port as previously discussed. A single protocol address is assigned to this common virtual interface. Also, a single team MAC address is assigned to the team from the set of MAC addresses assigned to each of the adapter ports of the team. Thus, other devices on the network see the team of adapter ports as a single virtual adapter port.
The throughput of the individual port members of the team can be aggregated for data transmitted from and received by the network device employing the team, depending upon the nature of the team configured. Throughput aggregation is commonly optimized using one of a number of known load-balancing algorithms, executed by the teaming driver, to distribute frames between the teamed NIC ports. The use of aggregated teamed adapter ports also inherently provides fault tolerance because the failure of one of the aggregated links does not eliminate the entire link. The aggregation of network interface resources through teaming is particularly beneficial in applications such as servers, as the demand for increased throughput and reliability of a network connection to a server is typically high.
Teams of network resources can be of various types providing different benefits. Network fault tolerant (NFT) teams commonly employ two or more network adapter or NIC ports redundantly coupled to the same network through a switch. One port is configured to be “active” and is designated as the “primary” adapter port. Each of the remaining members of the team is placed in a “standby” or “inactive” mode and is designated as a “secondary” member of the team. The primary adapter port is assigned a team MAC address from the set of MAC addresses associated with each of the team members. The secondary members are each assigned one of the remaining MAC addresses of the set. A NIC port in standby mode remains largely idle (it is typically only active to the limited extent necessary to respond to system test inquiries to indicate that it is still operational) until activated in a failover process. Failure detection and failover processes are typically executed by the teaming driver. Failover replaces the failed primary adapter port with one of the secondary team members, rendering the failed adapter port idle and secondary while activating one of the secondary adapters and designating it as the new primary for the team. In this way, interruption of a network connection to a critical server may be avoided notwithstanding the existence of a failed network adapter card or port.
Transmit load-balanced (TLB) teams typically aggregate and load-balance data transmitted from two or more active members of the team to other devices over the network in accordance with some load-balancing policy executed by the teaming driver. Several types of load-balancing algorithms may be employed with the teaming driver typically executing the algorithm. As with the NFT teams described above, only one of the active team members is designated as the primary for the team. Because the primary is the only member of the team that has been assigned the team MAC address, and this single MAC address is the one by which all devices on the network communicate with the team, it necessarily handles all of the data received by the team from the network. As a result, no aggregation of the receive traffic is available. TLB teams are particularly useful in applications where the transmit traffic is significantly greater than the traffic received by the team. One such application is a database server that provides data to a large number of clients in response to a relatively smaller amount of request traffic generated by those clients.
Switch-assisted load-balanced (SLB) teams are able to aggregate both transmit and receive data over all active team members. This is accomplished through a special switch interposed between the team and the network that has the intelligence to create a single virtual port for all of the physical ports coupling the team adapters and the switch. In this case, no adapter is designated as the primary and each team adapter is assigned the same team MAC address. The switch recognizes all packets it receives containing the team MAC address as being destined for the virtual port. The switch routes each such packet to one of the port members of the virtual port based on a load-balancing algorithm executed by the switch. The transmit data is typically load-balanced by the teaming driver in the manner used for TLB teams. SLB teams also provide fault tolerance by default, as team members that cease to function as a result of a fault will be inactivated and only the aggregated throughput of the team will be reduced as a result.
Certain network configurations are designed to achieve redundancy of connections between a system and the network using multiple coupling devices such as switches. Switch redundant configurations coupled to a server employing redundant links using a TLB or NFT team can result in members of the adapter team being coupled to the network through a different one of the redundant switches (and thus through separate paths of the network). To ensure that all team members are coupled to the same broadcast domain (i.e. same layer-2 network or subnet), these switch-redundant configurations require that all of the redundant devices (and therefore the team members) ultimately be interconnected in some way—either directly or by way of uplinks to a common third device (e.g. a backbone or core switch).